The present invention relates to a steel laminate gasket, more particularly a steel laminate gasket of a very thin type.
A conventional steel laminate gasket is constructed by laminating several plates, and is provided with a complicated sealing portion around a hole to be sealed. Consequently, it is difficult to manufacture a steel laminate gasket with light weight. Also, productivity of a steel laminate gasket is poor. As a result, a cost of a steel laminate gasket is expensive than the other gaskets.
In a small engine, a gasket must be light in weight and be manufactured at a low cost. However, as explained above, a conventional steel laminate gasket is heavy and expensive, so that a conventional steel laminate gasket is not usually used for a small size engine. Cost and heavy weight prevent a conventional steel laminate gasket from being used in a small size engine.
FIGS. 1-3 show conventional steel laminate gaskets. A gasket 10 as shown in FIG. 1 comprises an upper plate 11 having a curved portion 12 and a flange 13, and a lower plate 14, an end of which is situated inside the flange 13. Two inner plates 15, 16 with beads 15a, 16a are situated between the upper and lower plates 11, 14. Also, a plate 17 is situated between the upper plate 11 and the inner plate 15, and a plate 18 is situated between the lower plate 14 and the inner plate 16. A plate 19 is also situated between the inner plates 15, 16.
In this example, seven plates constitute one gasket. Further, this type of a gasket requires at least one surface pressure regulation plate to eliminate excess high pressure at a sealing portion, i.e. an area around the beads 15a, 16a. Namely, the surface pressure regulation plate receives tightening pressure together with the sealing portion to protect the sealing portion. In this example, the plates 17, 18 operate as surface pressure regulation plates. If the gasket 10 is tightened without the plates 17, 18, for example, strong tightening pressure is applied to the sealing portion, so that the sealing portion may, in an extreme situation, be broken.
A gasket 20 as shown in FIG. 2 comprises an upper plate 21 having a curved portion 22 and a flange 23, and a lower plate 24 having a stepped portion 25. A wire 26 is situated around the curved portion 22. Two inner plates 27, 28 and a plate 29 operating as a surface pressure regulation plate are situated between the upper and lower plates 21, 24. The plate 29 receives tightening pressure together with a sealing portion around the wire 26 to protect the sealing portion.
These conventional steel laminate gaskets are heavy, and include complicated sealing portions. Therefore, these gaskets can not be used for a small size engine with light weight.
On the other hand, a light weight gasket is disclosed in Japanese Utility Model Publication No. 59-188955 published on Dec. 14, 1984. A gasket disclosed in 59-188955 is shown in FIG. 3. The gasket 30 is designed to be used as a head gasket, which comprises a base plate 31 with a bead 31a, and a plate 32 situated on the base plate 31. The gasket 30 operates as intended when the gasket is used to seal around a low pressure area. However, since the bead 31a seals around a hole, the bead 31a can not provide high sealing pressure when tightened. Therefore, the gasket 30 can not be used for sealing a high pressure area.
Accordingly, one object of the present invention is to provide a steel laminate gasket, which is light in weight and simple in structure.
Another object of the present invention is to provide a steel laminate gasket as stated above, which can seal high and low pressure areas easily.
A further object of the present invention is to provide a steel laminate gasket as stated above, which can be easily and economically manufactured.
Further objects and advantages of the present invention will be apparent from the following description of the invention.